A 16 cylinder, direct injection, 5 valves-per-cylinder, engine develloped by VW/Audi that produces roughly 650 hosepower. There are however, versions of the engine that produce 800 and 1001 horsepower. The 1001 horsepower version sporting either a supercharger or four (yeah four!) exhaust turbochargers. The engine has a displacement of 7993 cc. It has four overhead camshafts with variable valve timing. The engine gets its W shape from "two very close-set banks of eight cylinders apiece joined at 90 degrees form the heart of this 736 kW / 1001 bhp 16-cylinder unit." Depending on who you ask, the engine either has a total of either 80 or 64 valves to contol intake and exhaust (of course 64 valves would mean only 4 valves per cylinder). "The fuel is injected via electromagnetic injection valves directly into the combustion chambers on the principle of FSI (fuel stratified injection), which is highly efficient and reduces emissions." The engine also makes an absolutely amazing amount of torque: 885 lb/ft between 2,200 and 5,500 rpm.
The engine is used in a few concept cars. These include the 2003 Bugatti Vayron and the creatively named Audi W16. Both of these have the engine mounted in the rear and use cameras and color monitors instead of a rear-view mirror.
Here is a picture of the engine.
http://www.vwvortex.com/news/02_01/02_27/geneva_01/veyron/engine.jpg
Quotations from: http://www.vwvortex.com/news/02_01/02_27/geneva_01/veyron/index.shtml